For better or worse, most people's photos never get transferred to a computer. Heck, there's a ton of people who don't have a non-phone computing device. Pushing their photos to the cloud so they see them after their current device dies is better than working on a new filesystem that allows for multiple host simultaneous access and porting that to everything. I could make a huge list of more tractable things that this hypothetical team could work on to make Android better for way more people.

Top on my list would be getting it so the touch screen just works every time. I can't count the number of times I've had to turn the screen off and on, because the touch screen came up in a way that I can't swipe up to get the code entry because swiping from the bottom to the top of the screen doesn't move it enough. I've had this happen on pretty much all my androids.

Things like booting faster would actually be nice. Especially since sometimes phones reboot in pockets. Setting up applications for faster starting would be amazing. It's not all in Google's court, but a basic hello world with the Android IDE starts up rather slow, even if you've noticed you need to compile a release build.